"Thinking that is governed by feeling I do not regard as intuitive thinking, but as a thinking dependant on feeling; it does not follow its own logical principle but is subordinated to the principle of feeling. In such thinking the laws of logic are only ostensibly present; in reality they are suspended in favour of the aims of feeling."
-Carl Jung [Psychological types, page 482]
For INTP, this would seem like Fi(8th function according to this), for ENTJ it would seem like Fe(8th), for INTJ it would seem like Fe(7th) and for ENTP it would seem like Fi(7th).
But its not 7th or 8th function, its just thinking unconsciously following feeling.
Same can happen with other functions:
"Fusion of psychological functions, of thinking with feeling, feeling with sensation, feeling with intuition, and so on, is archain."
(Psychological types page 413)
These functions, which are fused with other functions are undeveloped/undifferentiated.
"Differentation means the development of differences, the separation of parts from the whole. So as long as a function is still so fused with one or more other functions -thinking with feeling, feeling with sensation, etc- that it is unable to operate on its own, it is archain condition i.e., not differentiated, not separated from the whole as a special part and existing by itself.[my note, differentation isnt yes or no thing, but function can be more or less differentiated]. Without differentation direction is impossible, since the direction of a function towards a goal depends of elimination of anything irrelevant. Fusion with the irrelevant precludes direction; only a differentiated function is capable of being directed."
[Psychological types page 424]
As a conclusion, shadow functions arent your normal functions in opposite orientation, but any of the 4 function that is in archain condition, fused with other functions.